When he was in prison on Robben Island, Nelson Mandela spent long periods engaged in hard manual labor— breaking rocks into gravel, and working in a quarry. You would think that this would be enough exercise for a day, but during these years Mandela also maintained a strict workout regimen inspired by his youth as a boxer. Why in the world would someone who’s breaking rocks do this? The answer reveals something about the nature of deliberate rest.

As he later recalled in his memoir Long Walk to Freedom:

I attempted to follow my old boxing routine of doing roadwork and muscle-building from Monday through Thursday and then resting for the next three days. On Monday through Thursday, I would do stationary running in my cell in the morning for up to forty-five minutes. I would also perform one hundred fingertip push-ups, two hundred sit-ups, fifty deep knee-bends, and various other calisthenics.

The state wanted to use manual labor to break its prisoners, and— as with all prisons— dictate the terms of prisoners’ existence. For Mandela, continuing his old routine was a way of resisting this, and declaring that he would continue to be in command of his self. Further,

I have always believed exercise is a key not only to physical health but to peace of mind. Many times in the old days I unleashed my anger and frustration on a punchbag rather than taking it out on a comrade or even a policeman. Exercise dissipates tension, and tension is the enemy of serenity. I found that I worked better and thought more clearly when I was in good physical condition, and so training became one of the inflexible disciplines of my life. In prison, having an outlet for my frustrations was absolutely essential.

So staying in shape was also a way of staying mentally sharp— which in turn was another poke at his captors.

Why is Mandela’s routine an example of deliberate rest? It’s something that he does in order to maintain his mental agility and intelligence: it’s exercise intended to have cognitive payoffs. It’s also an example of (to borrow a phrase from Clifford Geertz, among others) deep play: it’s an activity that has significant symbolic meaning for Mandela, that connects him to his previous life before prison, and constitutes a show of resistance against his prison wardens and the state. And it’s an activity that connects to his broader life: it provides him the peace of mind and clear thinking he needed to survive prison life, and to emerge as a leader despite the harsh conditions of Robben Island.